No way Maplewood is the best farmers market. It's nice being on a Wednesday evening, but the selection is limited and the atmosphere is super yuppie. Tower Grove's is good, but I think Ferguson may be the best kept secret.
All local growers, lots of organic items (including meat and cheese), great chef demos and samples, and a wide selection in general. They also have live music and the occasional cooking contest with prize money. Good atmosphere, reasonable prices.
Ride the bike trail from Metro to get there. Two miles round trip - an interesting, peaceful ride.